Kai graduated in 1940 from Stuyvesant High School in New York City and that same year began his career as a professional trombonist with Shorty Allen's band.

Subsequently, he played with Sonny Dunham and Alvino Rey,[2] until he entered the United States Coast Guard during World War II.

His best selling recording from this period is "More," the theme from the movie Mondo Cane, which reached number 8 in the Billboard Hot 100 and remained his only entry here.

[4] Arranged and conducted by Claus Ogerman, "More" featured what is probably the first appearance of the French electronic music instrument the ondioline on an American recording.

[6] With J. J. Johnson With Ralph Burns and Leonard Feather With Quincy Jones With Stan Kenton With King Pleasure With Pete Rugolo With Zoot Sims With Sarah Vaughan With others